CODEWITHSUNDEEP
c++types
qazwsx
qazwsx

Reputation: 26888

Is `int` by default `signed long int` in C++?

Is int by default signed long int in C++?

Is it platform and/or compiler dependent? If so, how?

[EDIT]

Are any of the following guaranteed to be duplicate?

signed short int
signed int
signed long int
signed long long int
unsigned short int
unsigned int
unsigned long int
unsigned long long int

Upvotes: 13

Views: 19953

Answers (6)

Dietmar Kühl
Dietmar Kühl

Reputation: 153820

All of the integer types are different, i.e. you can safely overload functions for all of them and you won't get any conflict. However, some times use the same number of bits for their representation. Even if they use the same number of bits signed and unsigned types always have a different range. Except for char, using any integer type without signed is equivalent to using it with signed, i.e. signed int and int are equivalent. char is a different type as signed char and unsigned char but char has the same representation and range of either signed char or unsigned char. You can use std::numeric_limits<char>::is_signed to find out which it uses.

On to the more interesting aspects. The following conditions are all true:

  • 7 <= std::numeric_limits<signed char>::digits
  • sizeof(char) == 1
  • sizeof(char) == sizeof(signed char)
  • sizeof(char) == sizeof(unsigned char)
  • 15 <= std::numeric_limits<short>::digits
  • sizeof(char) <= sizeof(short)
  • sizeof(short) <= sizeof(int)
  • 31 <= std::numeric_limits<long>::digits
  • sizeof(int) <= sizeof(long)
  • 63 <= std::numeric_limits<long long>::digits
  • sizeof(long) <= sizeof(long long)
  • sizeof(X) == sizeof(signed X)
  • sizeof(signed X) == sizeof(unsigned X)

(where "X" is one of char, short, int, long, and long long).

This means that the size of all integer types can be the same as long as this types hold at least 64 bits (and apparently the Cray X-MP was such a beast). On contemporary machines typically sizeof(int) == sizeof(long) but there are machines where sizeof(int) == sizeof(short). Whether long is 32 or 64 bits depends on the actual architecture and both kinds are currently around.

Upvotes: 14

Ben Voigt
Ben Voigt

Reputation: 283624

plain int is signed, whether or not it's the same size as long int is platform-dependent.

What's guaranteed is that

sizeof (int) <= sizeof (long)

and int is big enough to hold at least all values from -32767 to 32767.

What the standard says: (section [basic.fundamental]:

There are five standard signed integer types : signed char, short int, int, long int, and long long int. In this list, each type provides at least as much storage as those preceding it in the list. There may also be implementation-defined extended signed integer types. The standard and extended signed integer types are collectively called signed integer types. Plain ints have the natural size suggested by the architecture of the execution environment; the other signed integer types are provided to meet special needs.

Upvotes: 25

Johannes Schaub - litb
Johannes Schaub - litb

Reputation: 506905

The long and short modifiers are not exactly like signed and unsigned. The latter two can be put on any integer type, but if you leave them off, then signed is the default for each integer type (except char). So int and signed int are the same type.

For long and short, if you leave them off, neither is chosen, but the resulting type is different. long int, short int and int are all different types, with short int <= int <= long int.

The int after long, short, signed and unsigned is optional: signed int and signed are the same type.

Upvotes: 5

lapk
lapk

Reputation: 3918

In C++ int is signed int by default, so there is no problem with that. However, int and long int are different types in C++, so this is not the same from the point of view of the language. Implementation of int and long int is platform/compiler specific - they are both integral types which might be identical. The only limitation C++ standard imposes is that sizeof( long int ) >= sizeof( int ).

Upvotes: 2

user541686
user541686

Reputation: 210402

signed and int are both the same as signed int by default.

Neither is the same type as signed short int or signed long int.

Upvotes: 1

cHao
cHao

Reputation: 86506

Plain int is equivalent to signed int. That much is standard. Anything past that is not guaranteed; int and long are different types, even if your particular compiler makes them the same size. The only guarantee you have is that a long is at least as big as an int.

Upvotes: 8

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